Method and apparatus for performing handover in wireless telecommunication system

Abstract

The present invention relates to a method and apparatus for performing a handover in a wireless telecommunication system. The present invention measures a signal strength of a serving base station and a neighbor base station, and triggers an anchor base station update when the signal strength of the neighbor base station is higher than the signal strength of the serving base station by a predetermined triggering value, thereby preventing the signal strength of the serving base station from being rapidly decreased and capable of efficiently performing a handover.

1 . A method of performing handover in a wireless communication system, the method comprising the steps of:
 a) receiving a Downlink Channel Descriptor (DCD) message from a serving base station and acquiring Fast Base Station Switching (FBSS) information;   b) receiving a neighbor base station advertisement message from the serving base station and acquiring a neighbor base station information;   c) measuring the signal strength of the serving base station and the neighbor base station based on the neighbor base station information;   d) transmitting a handover request message to the serving base station, when the difference between the signal strength of the neighbor base station and the signal strength of the serving base station is a predetermined triggering value; and   e) transmitting a handover indication message to the serving base station and performing a handover by triggering an anchor base station update when a handover response message is received from the serving base station in response to the handover request message.   
   
   
       2 . The method of  claim 1 , wherein the triggering value is equal to or lower than the difference between a diversity set addition threshold value and a diversity set deletion threshold value. 
   
   
       3 . The method of  claim 1 , wherein the step d) transmits the handover request message to the serving base station, when the signal strength of the serving base station decreases below a diversity set deletion threshold value before the difference between the signal strength of the neighbor base station and the signal strength of the serving base station is equal to the predetermined triggering value. 
   
   
       4 . The method of  claim 1 , wherein the DCD message includes a trigger Type, Length and Value(TLV) information defined to trigger the anchor base station update when the signal strength of the neighbor base station is higher than the signal strength of the serving base station as much as the predetermined triggering value. 
   
   
       5 . The method of  claim 1 , wherein the step c) comprises:
 c1) transmitting a scanning request message to the serving base station;   c2) receiving a scanning response message from the serving base station in response to the canning request message; and   c3) measuring the signal strengths of the serving base station and the neighbor base station, based on the neighbor base station information and the scanning response message.   
   
   
       6 . The method of  claim 5 , wherein the signal strength is measured by using at least one of a Carrier to Interference and Noise Ratio (CINR), a Received Signal Strength Indication (RSSI), and a Real Time Difference (RTD). 
   
   
       7 . A method of performing handover in a wireless communication system, the method comprising the steps of:
 a) receiving a Downlink Channel Descriptor (DCD) message and a neighbor base station advertisement message from a serving base station and acquiring a signal strength of the serving base station and a neighbor base station;   b) transmitting an anchor switching indication message to the serving base station through a fast feedback channel, when the signal strength of the neighbor base station is higher than the signal strength of the serving base station as much as a predetermined triggering value; and   c) performing a handover by triggering the anchor base station update when an anchor switching information message for permitting the anchor switching in response to the anchor switching indication message is received from the serving base station.   
   
   
       8 . The method of  claim 7 , wherein the step b) transmits the anchor switching indication message to the serving base station, when the signal strength of the serving base station is lower than a diversity set deletion threshold value before the signal strength of the neighbor base station becomes higher than the signal strength of the serving base station as much as the predetermined triggering value and the triggering value is equal to or lower than the difference between a diversity set addition threshold value and a diversity set deletion threshold value. 
   
   
       9 . The method of  claim 7 , wherein the DCD message includes a trigger Type, Length and Value (TLV) information defined to trigger the anchor base station update, when the signal strength of the neighbor base station is higher than the signal strength of the serving base station as much as the predetermined triggering value. 
   
   
       10 . The method of  claim 7 , wherein the DCD message includes an Anchor Switch Report (ASR) Slot Length (M) and Switching Period (L) information, and the fast feedback channel is established based on the Anchor Switch Report (ASR) Slot Length (M) and Switching Period (L) information. 
   
   
       11 . The method of  claim 7 , wherein the step a) of acquiring a signal strength of the serving base station and a neighbor base station comprises:
 a1) transmitting a scanning request message to the serving base station;   a2) receiving a scanning response message from the serving base station in response to the canning response message; and   a3) measuring the signal strengths of the serving base station and the neighbor base station, based on the neighbor base station information and the scanning response message.   
   
   
       12 . A method of performing handover in a wireless communication system, the method comprising the steps of:
 a) measuring signal strengths of a serving base station and a neighbor base station; and   b) performing a handover when the signal strength of the neighbor base station is higher than the signal strength of the serving base station as much as a predetermined triggering value.   
   
   
       13 . The method of  claim 12 , wherein the step b) transmits a handover indication message or an anchor switching indication message to the serving base station, when the signal strength of the serving base station is lower than a diversity set deletion threshold value before the signal strength of the neighbor base station is higher than the signal strength of the serving base station as much as the predetermined triggering value, and the triggering value is equal to or lower than the difference between a diversity set addition threshold value and a diversity set deletion threshold value. 
   
   
       14 . The method of  claim 12 , wherein the step b) includes a step of triggering an anchor base station update through a MAC management message or a fast feedback channel. 
   
   
       15 . The method of  claim 12 , wherein, after step a), further comprising b′) performing a diversity set update based on the signal strength of the neighbor base station. 
   
   
       16 . The method of  claim 15 , wherein the diversity set update is performed by adding the neighbor base station to the diversity set when the signal strength of the neighbor base station which is not included in the diversity set is higher than a predetermined diversity set addition threshold value, and deleting the neighbor base station from the diversity set when the signal strength of the neighbor base station which is included in the diversity set is lower than a predetermined diversity set deletion threshold value. 
   
   
       17 . An apparatus of performing handover in a wireless communication system, the apparatus comprising:
 a signal strength measuring unit for measuring a signal strength for a serving base station and a neighbor base station;   a MAC management message processing unit for transmitting and receiving a MAC management message for the serving base station;   an anchor base station update processing unit for triggering an anchor base station update; and   a FBSS processing unit for requesting the anchor base station update processing unit to trigger the anchor base station update, when the signal strength of the neighbor base station is higher than the signal strength of the serving base station by a predetermined triggering value, based on a DCD message transmitted from the MAC management message processing unit.   
   
   
       18 . The apparatus of  claim 17 , wherein the triggering value is lower than a difference value between a diversity set addition threshold value and a diversity set deletion threshold value. 
   
   
       19 . The apparatus of  claim 17 , wherein the FBSS processing unit requests the anchor base station update processing unit to trigger the anchor base station update, when the signal strength of the serving base station is lower than a diversity set deletion threshold value before the signal strength of the neighbor base station becomes higher than the signal strength of the serving base station as much as the predetermined triggering value. 
   
   
       20 . The apparatus of  claim 17 , wherein the DCD message includes a trigger Type, Length and Value (TLV) information defined to trigger the anchor base station update when the signal strength of the serving base station is lower than the signal strength of the neighbor base station as much as or beyond the predetermined triggering value. 
   
   
       21 . The apparatus of  claim 17 , wherein the signal strength is measured by using at least one of CINR, RSSI, and RTD. 
   
   
       22 . The apparatus of  claim 20 , wherein the DCD message includes a MAC Management Message Type (MMT) field, a Configuration Change Count (CCC) field, and a TLV field for FBSS, while the trigger TLV information is included in the TLV field. 
   
   
       23 . The apparatus of  claim 22 , wherein the TLV field further includes a diversity set addition threshold value (H_Add_Threshold), a diversity set deletion threshold value (H_Delete_Threshold), and an Anchor Switch Report (ASR) Slot Length (M) and Switching Period (L) information. 
   
   
       24 . The apparatus of  claim 22 , wherein the trigger TLV information includes a Type, Function and Action (TFA), a Trigger Value (TV), and a Trigger Averaging Duration (TAD).